Falak lists the four events involved in the formation of sinkholes.

w - acidic rainwater dissolves the limestone bedrock.
x - large cavities form in the bedrock.
y - natural holes and cracks become bigger.
z - the ceiling collapses due to the weight of sediment.

which list shows the correct order of these events in the formation of sink holes?

a) w, x, y, z
b) w, y, x, z
c) w, z, y, x
d) w, z, x, y

B)  W, Y, X, Z

Explanation:

Rain water absorbs carbon dioxide to change into mild acid water due to formation of carbonic acid. The acid water moves into the soil through spaces and cracks. Slowly it dissolves limestone and creates many cavities. Pores and cracks get enlarged.  As more limestone is dissolved. When the land surface above collapses into the cavities sink holes are formed. Too much extraction of ground water may responsible for formation of sink holes.